Semiconductor lasers are utilized in a wide variety of applications. The relatively small size, low input power requirements and high power conversion efficiencies of semiconductor lasers make them well-suited for fiber-optic applications.
Conventional semiconductor laser configurations are implemented as diodes typically consisting of multiple epitaxial layers provided upon an appropriate substrate, such as indium phosphide. An active layer, such as indium gallium arsenide phosphide is sandwiched between n and p-type cladding layers of the substrate material in some configurations. Opposing metal contacts are provided about the structure and a bias current is applied to the contacts to generate light at a wavelength determined by the energy gap of the active layer.
Semiconductor lasers are modulated to communicate information in fiber-optic applications. Intensity modulation is a common type of modulation in optical communication systems. One example is digital pulse code modulation wherein the laser is directly driven by the baseband signal. Subcarrier multiplexed systems are also frequently utilized wherein the laser is driven by an RF or microwave subcarrier modulated by a data signal.
Demands for high speed network applications continue to increase as more people and businesses rely upon networks for fast, reliable communication of voice and data. Further, broadband optical systems benefit from using lasers having wider bandwidths than the system bandwidth to provide flatter and more efficient responses and reduction in intensity noise, distortion and phase deviation. Accordingly, it is desired to provide systems with the highest possible bandwidths.
Some laser configurations have bandwidths limited to a few gigahertz by a number of factors including diode resistance, capacitance and bond-wire inductance, for example. A further limitation upon bandwidth includes the inherent restrictions imposed by modulating the total photon population of the laser cavity. When modulation frequencies exceed the normal bandwidth of a laser, the total photon population no longer responds to the input modulation. There exists a need to provide improved devices and methodologies which avoid limitations experienced with conventional designs.